Experimental Investigation of Lift and Drag Characteristics of a Typical MAV under Propeller Induced Flow

Abstract

Experiments were conducted on a micro air vehicle (MAV) model in a low speed wind tunnel to study the actual lift and drag experienced by the model under propeller induced flow by separating out the thrust force generated by the propeller by decoupling the motor-propeller from the model and mounting it on a second arrangement with minimal flow interference. Tests were conducted on the model at actual flight conditions -at a freestream velocity of 9 m/s (Re = 135000 based on root chord) with the propeller running at speeds ranging from 8000 to 10000 rpm. The lift and drag coefficients obtained from the model with decoupled motor-propeller arrangement are compared to those obtained from the model with attached motor-propeller for the same test conditions and justification is made in favor of the former method. Effects of propeller induced flow with respect to an increase in propeller rpm on the lift and drag characteristics of the model were also studied. Higher C L at higher angle of attack and increased C D were observed for the model under propeller induced flow. With an increase in propeller rpm, the effects seen in C L and C D are increased further.Reynolds number rpm rotation per minute V ∞ freestream velocity α angle of attack (degree) INTRODUCTIONResearch into the field of MAVs has been active for a long time, yet understanding of its aerodynamics are more challenging in certain aspects. A plethora of literature exist on the aerodynamic investigation of MAVs but very few literature [1-3, 6-9] are available which addresses the aerodynamics of MAVs under propeller induced flow. Null, Noseck and Shkarayev [1] in their attempt to study the effects of propeller induced flow on the aerodynamics of MAV, adopted a test methodology in which the dynamic thrust data were collected at the test velocity from the motor/propeller mounted on a pylon at 0 o angle of attack and the data was resolved into horizontal and vertical component for all the angles of attack the propelled MAV model was tested. To decouple the direct forces created by the propeller on the total lift and drag measured on MAV model, the vertical component contributing to overall lift is subtracted from the lift data and the horizontal component contributing to forward thrust is added to the total drag data of the propelled MAV model. The results obtained shows that the propeller induced flow caused higher magnitudes of lift at higher angles of attack & delayed stall, but a detrimental effect on the drag coefficients, and a subsequent decrease in the lift-to-drag ratio at low angles of attack. However, they concluded that, due to the way the aerodynamic coefficients were calculated, the effects in the aerodynamic coefficients are partly a mathematical phenomenon. Experiments by Gamble and Reeder [2] on a MAV to study the propeller-wing interaction were

Effect of propeller-induced flow on the performance of biplane micro air vehicle dynamics

“…11 Similarly, experiments at Reynolds number 135,000 with motor rotation in the range of 8000-10,000 r/min with 300 mm wingspan model showed an increase of C L at a higher AoA and increase of C D with the propulsive flow. 12 The effects of propeller induced flow on C L and C D further increases with an increase in the speed of motor rotation. Similarly, the increase of lift, drag, and stall AoA with increasing slipstream to free stream velocity ratio is observed during wind test on a model with a wingspan of 252.0 mm and a chord length of 142.6 mm with a propeller diameter of 5.5 inches in the velocity range of 5-15 m/s.…”

“…8 The size of the propeller dimension to the wing dimension is comparable in the case of propeller-driven MAV; hence, the effect of the propeller-induced flow on the overall aerodynamics is quite significant as it influences the flow transition, 9 flow separation, flow reattachment and formation of laminar separation bubbles. 10 The important parameters that are affected by the propulsive forces are stall angle of attack (AoA), 11 lift coefficient ( C L ), and drag coefficient (CD), 12 the slope of lift versus AoA curve, 13 LD ratio, 14,15 pitching moment, 16 etc. Propeller flow also influences the transition from laminar flow to turbulent flow.…”

Modeling and Closed Loop Flight Testing of a Fixed Wing Micro Air Vehicle

“…Hence, a conventional aircraft modeling techniques that do not take into account of propeller wake are inadequate to model the aerodynamic forces acting on MAV. The aerodynamic effects of propeller flow on MAV and small UAV are studied in [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. The influence of propeller wake on the lift, drag and wing stall characteristics is reported in [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ].…”

Computational Study of a Lifting Surface in Propeller Slipstreams

“…12,13 The use of small distributed propellers upstream of the wing leads to an increase in aerodynamic lift. [14][15][16][17] The performance benefits of these wings are directly applicable to the takeoff and landing flight regimes due to a higher achievable lift curve slope and C L max . However, recent computational studies have shown the increase in aerodynamic drag of the wing due to slipstreams.…”

“…However, recent computational studies have shown the increase in aerodynamic drag of the wing due to slipstreams. 16,17 Wingtip mounted propellers which improve the aerodynamic efficiency of the wing 18,19 can be used to provide thrust during cruise with the inbound propeller shut and folded. 16 Preliminary wing design and aircraft performance tools for V/STOL aircraft with distributed propeller system such as those developed by Bronz et al 20 require better theory to understand the aerodynamic interaction between a propeller and a wing.…”